1. Field of the Invention
The present invention relates generally to a magnetic sensor, and more particularly to a magnetic sensor comprising a sensor chip having a magneto-resistive effect device, said sensor chip being sealed up in a resin.
2. Description of the Prior Art
In recent years, magneto-resistive effect devices (MR devices) such as those of the giant magneto-resistive effect (GMR), tunnel magneto-resistive effect (TMR) and anisotropic magneto-resistive effect (AMR) types have been applied to the magnetic sensor field. Typically, the GMR or TMR type magneto-resistive effect devices comprise a magnetization-fixed layer having a direction of magnetization fixed relative to an external magnetic field (pinned magnetic layer) and a magnetization-free layer having a direction of magnetization variable depending an external magnetic field (free magnetic layer). As an external magnetic field acts on such a magneto-resistive effect device, it causes the direction of magnetization of the magnetization-free layer to change, generating a change in the relative angle with the direction of magnetization of the magnetization-fixed layer. The change in the direction of magnetization appears as a change in the magneto-resistance of the magneto-resistive effect device, by which the intensity of the external magnetic field may be detected.
A magnetic sensor making use of such a magneto-resistive effect device has a typical structure in which a sensor chip including a magneto-resistive effect device placed on a base member, desired wirings or the like connected to the terminals of the sensor chip are sealed up in a resin member for their protection, and magnetic sensors of such a structure are used for angle sensors, etc. (Unexamined Patent Publication Nos. 2007-263951, 2010-78360 and 2010-145285).
However, a problem with a magnetic sensor having such a resin-sealed structure is that upon subjected to an external force, there is stress applied to the sensor chip via the resin member, resulting in a change in the sensor chip characteristics. For instance, with an angle sensor having a built-in magnetic sensor harnessing the magneto-resistive effect device, the angle measured while stress is applied to the sensor chip tends to have errors; a problem with that angle sensor is that it cannot be used in fields of detecting the angle of rotation, etc. of a rotating shaft with high precision in a stable manner. On the other hand, the TMR type magneto-resistive effect device is higher in MR ratios than, and much superior in output performance to, the AMR or GMR type magneto-resistive effect device, but, to the contrary, it is sensitive to stress acting on the sensor chip. For this reason, a magnetic sensor making use of the TMR type magneto-resistive effect device in particular is still required to have a structure less susceptible to stress, although depending on its purpose.
The situations being like this, an object of the present invention has for its object to provide a magnetic sensor having a structure in which a sensor chip including a magneto-resistive effect device is sealed up in a resin member, and which enables the sensor chip to perform well in a good state.